This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Fatty acid synthase (FASN) is the enzyme that catalyzes the de novo synthesis of fatty acids in cells. FASN is up-regulated in solid tumors, and its overexpression has been associated with poor prognosis in breast cancer patients. FASN regulates the expression of the human epidermal growth factor receptor 2 (her-2 also known as c-erbB-2) gene. We have recently found that FASN forms a complex with phosphorylated EGFR and HER-2. Our hypothesis is that FASN phosphorylation is critical for HER-2 signaling in breast cancer cells. The specific aim of this proposal is to identify the FASN/HER-2 and FASN/EGFR phosphorylation sites in HER2-overexpressing breast cancer cells using immunoprecipitation, immobilized metal-ion affinity chromatography (IMAC), and high resolution LC-MS/MS.